Noise suppression



Sept. 22, 1970 I v ROYER EIAL 3,530,349

NOISE SUPPRESSION Filed May 20. 1968 a 6 a I 6 r;

"FIGJ" v 4 v 5 /0/ has) a F 3' F #3 ma fin 41?] 4, I'K/T-SCA 06641 B. 207i United States Patent US. Cl. 318227 4 Claims ABSTRACT OF THE DISCLOSURE In an alternating current device such as an electric motor or fluorescent lighting ballast with dimmer, wherein a multiturn coil is electrically connected to a source of alternating current through a solid state switch by which the voltage to the coil is regulated, the coil is split into two parts and the solid state switch is electrically interconnected to and between the split parts of the coil. This has been found to reduce both radio frequency interference and audible noise, both of which are embraced Within the term noise as used herein.

BACKGROUND OF THE INVENTION In many inductive devices such as permanent split capacitor, split phase and shaded pole motors, dimmer ballast for fluorescent lighting fixtures and the like, a solid state switch is commonly used to vary the RMS voltage to a coil. In a typical solid state switch arrangement, a triac is electrically connected in series between a source of alternating current and the coil. The firing of the triac is controlled by a triggering diode the operation of which is controlled by a variable resistor and a capacitor, so arranged that the greater the resistance, the more slowly the capacitor charges, and the later in each half cycle the triggering diode acts to fire the triac. If the variable resistor is set so that it offers little resistance, the capacitor will charge substantially with the line voltage, and the triggering diode will be energized very near the beginning of each half cycle.

Similar arrangements, using, for example, a pair of silicon controlled rectifiers, or silicon controlled switches, or other devices serving as bidirectional controlled rectifiers are also commonly used and well known to the art. All of these devices and their equivalents are encompassed by the term solid state switch as used hereinafter.

All of these solid state switches have the common characteristic of generating a large amount of radio frequency power, which interferes seriously with radio reception. It has also been found that all these switches are sources of audible noise in the magnetic structure of devices such as fractional horsepower electric motors.

One of the objects of this invention is to provide a means for reducing radio frequency interference and audible noise in an AC device in which a multiturn coil in a magnetic device is electrically connected to a solid state switch.

Another object is to provide such means which can be located and connected internally of the housing of the device.

Another object is to provide such a means which is inexpensive, simple, and more effective than any practical device known heretofore to accomplish its purpose.

Other objects will become apparent to those skilled in the art in the light of the following description and accompanying drawings.

SUMMARY OF THE INVENTION In accordance with this invention, generally stated, in an alternating current device wherein a multi-turn coil is 3,530,349 Patented Sept. 22, 1970 ice electrically connected to a source of alternating current through a solid state switch by which the voltage to the coil is regulated, the coil is split into two parts and the solid state switch is electrically connected to and between the split parts of the coil.

DESCRIPTION OF THE DRAWING In the drawing, FIG. 1 is a diagrammatic view of one illustrative example, in the form of an electric motor circuit, of device of this invention; and

FIG. 2 is a diagrammatic view of another illustrative example, in the form of a dimming fluorescent lamp circuit, of device of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawing, and especially to FIG. 1 for one illustrative embodiment of device of this invention, reference numeral 1 indicates a permanent split capacitor motor having a main winding 2 and an auxiliary winding 3. A capacitor 4 is electrically connected in series with the auxiliary winding 3 and the auxiliary and main windings are connected in parallel to a source 5 of single phase alternating current, by means of conductors 6 and 7.

The main winding 2 is split, in this embodiment, into two equal parts 12 and 13. One end of the part 12 is electrically connected at 14 to the conductor 6. One end 15 of the part 13 is electrically connected to the conductor 7. The other end 16 of the part 12 is electrically connected to a conductor 18. The other end 17 of the part 13 is electrically connected to a conductor 19. Connected to and between the conductors 18 and 19, hence to and between the parts 12 and 13 of the main winding 2, is a triac 20. The triac 20 is conventional. When fired, it conducts as long as the current through it continues, turning off when the current reaches zero. It conducts in either direction, depending upon the polarity of the voltage at the time it is fired. In the embodiment shown, it is fired or caused to fire by a triggering diode 30, electrically connected by means of a conductor 32 to a conductor 33. The conductor 33 is electrically connected to and between a capacitor 34 and a variable resistor 35, which are electrically connected, in series with one another, to and between the conductors 18 and 19. A conductor 39 is electrically connected to and between a resistor 40 and a capacitor 41, which are electrically connected, in series with one another, to and between the conductors 18 and 19. A resistor 38 is electrically connected to and between conductors 33 and 39.

A commutating capacitor 45 and resistor 46 are also connected, in series with one another, to the conductors 18 and 19 and in parallel with the triac 20.

The commutating capacitor 45 and the capacitor 41 serve a useful function, but they do not form an essential part of the invention.

As far as the operation of the motor is concerned, the circuit acts in the same way as the conventional solid state switch controlled motor circuit. However, the placement of the solid state switch (triac) between the two parts 12 and 13 of the main winding, provides a very high impedance to the radio frequency power generated by the solid state switch, limiting the flow of radio frequency current and thereby limiting the conducted radio frequency current to an extremely low level as compared with conventional arrangements. Motor audible noise level also has been found to be reduced.

The size and character of the various components of the device shown in FIG. 1, may be conventional. Merely by way of illustration, and not by way of limitation, in a one-half horsepower, volt, single phase, permanent split capacitor motor, the triac 20 may be rated 15 amperes 2 00 v., the triggering diode 30, with V -=32 v., the

capacitor 34, 0.1 mfd. 200 v., the capacitor 41, 0.1 mfd. 200 v., the-capacitor 45, 0.05 mfd. 200 v., the resistor 40, 68,000 ohms, the resistor 46', 470 ohms, the resistor 38, 47,000 ohms, and the variable resistor 35, -15 0,000 ohms.

Referring now to FIG. 2 for another embodiment of device of this invention, reference numeral 101 indicates a dimmer equipped fluorescent lighting system. The system 101 includes a hot cathode rapid start fluorescent lamp 110, a ballast 100, a dimmer control circuit 104, and a source of alternating current, represented by conductors 105 and 106.

The ballast 100 includes coils 102 and 103. The coil 102 is split into two parts 112 and 113, between which the control circuit 104 is electrically connected. The coil part 112 is electrically connected to a conductor 118 and the coil part 113, to a conductor 119.

Between the conductors 118 and 119, are electrically connected in parallel a triac 120, a capacitor 134 and variable resistor 135, a resistor 140 and capacitor 141, and a capacitor 145 and resistor 146. A triggering diode 130 is electrically connected on one side to the gate terminal of the triac and on the other, to a conductor between the capacitor 134 and the variable resistor 135. A resistor 138 is electrically connected to and between conductors between the capacitor 134 and variable resistor 135 and resistor 140 and capacitor 141.

The effect of the splitting of the winding 102 in this aplication is the same as the effect of the splitting of the main winding 2 of the motor in the application shown in FIG. 1. The amount of radio frequency current is reduced to an extremely low level as compared with devices known heretofore.

Effective suppression of radio frequency interference and noise is accomplished as long as the winding split provides suflicient impedance to the radio frequency power to suppress the flow of radio frequency current from the solid state switch. The number of turns in each of the two portions of the winding may be substantially different than a 50/50 split and still do a very effective job of radio frequency interference suppression.

It will be apparent to those skilled in the art that the present invention has application to numerous other inductive devices, such as other forms of transformers, and dual value permanent split capacitor motors, and to such devices as soldering guns and the like.

Numerous variations in the construction and application of device of this invention, within the scope of the appended claims, will occur to those skilled in the art in the light of the foregoing disclosure.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

1. In an alternating current device wherein a multiturn coil is electrically connected to a source of alternating current and a solid state switch by which the voltage to the coil is regulated, the improvement comprising a first part of said coil electrically connected to said current source and electrically connected directly to said solid state switch, and a second part of .said coil electrically 1 connected to said current source and electrically connected directly to said solid state switch, said first coil part, solid state switch and second coil part being connected, in that order, in electrical series with one another, said coil parts providing suflicient impedance to radio frequency power to suppress the flow of radio frequency current from the solid state switch.

2. The improvement of claim 1 wherein the device is an electric induction motor and the coil is the main winding of said motor.

3. The improvement of claim 2 wherein the motor is a permanent split capacitor motor.

4. The improvement of claim 1 wherein the device is a fluorescent lamp circuit and the coil is a winding of a ballast transformer electrically connected in said circuit.

References Cited I UNITED STATES PATENTS 2,724,062 11/ 1955 Nolde 30791 XR 2,923,856 2/1960 Greene et a1. 3l5100 XR 3,335,291 8/ 1967 Gutzwiller 3073 05 XR OTHER REFERENCES AC Motor Speed Control, Mungenast, Dowling, Home Appliance Builder, August 1964, pp. 13-15, 38. ORIS L. RADER, Primary Examiner G. Z. RUEINSON, Assistant Examiner US. Cl. X.R. 

